Treatment of wood



ii'atented pa. i6,

TREATMENT OF WOOD Hamline Monroe Kvalnes, Wilmington, Del., as-

signor to E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware No Drawing. Application March 10, 1943,

Serial No. 478,666

Claims; (Cl. 117-148) This invention relates to the treatment of wood, and more particularly to a method for inhibiting dimensional changes therein induced by moisture and exposure.

it is an object of this invention to treat wood in order to inhibit dimensional changes therein induced by moisture and exposure. Another object is to provide a wood treatment composition which is of low cost and high activity in its ability to prevent or inhibit dimensional changes in wood. Another object is to provide a simple, stable woodtreating solution which is easy to. handle and which does not yield any substantial amount of precipitate during use. Other objects will be apparent hereinafter.

These objects are accomplished in accordance with this invention which provides a process for inhibiting dimensional changes in wood induced by moisture and exposure by impregnating such wood with a freshly-prepared, relatively concentrated solution of an active methylol urea compound, and then drying the wood, said compound having a composition of from 25 to 75 mole per cent of dimethylol urea and from '75 to 25 mole per cent of monomethylol urea.

It has been discovered that when wood is impregnated with freshly-prepared aqueous solutions of particular methylol urea compounds, especially sesquimethylol urea, which have been maintained in the active state as hereinafter more fully described, the wood is stabilized against diylol urea is employed, and has the composition. corresponding to an equimolar mixture of mono- However,

methylol urea with dimethylol urea. the activity of sesquimethylol urea for dimensionally stabilizing wood in accordance with the present invention is so much superior to any other methylol urea. and its stability is so great, that it has been assigned the name sesquimethylol urea which indicates its composition to be 1% methylol groups for each urea nucleus. By the expression active methylol urea compounds is meant a methylol urea within the prescribed composition limits which is freshly prepared immediately prior to its use, or which has been stored at a temperature not higher than about 60 F. for not longer than about three months. The aqueous solutions of the methylol urea compressure of several atmospheres up to 40 or 50 pound should likewise be freshly prepared, that is they should be made up immediately prior to the wood impregnation, or be no older than several days to not more than one week.

A relatively concentrated aqueous solution is employed for the wood impregnation, suitably.

from about 10 to 35% by weight of active methylol urea compound, and preferably within the more restricted range of from about 15 to 30 by weight of active methylol urea compound. Higher concentrations can be used up to about 40 or 45% by weight if the solution is heated, but in general such high concentrations are unnecessary.

The pH of the impregnating solution is within the neutral to alkaline range, and can even be mildly acid it promptly used. A pH of 5.0 to 11.0 is operative, and preferably the pH is kept within the mor restricted range of 7.0 to 9.0 for greatest stability of the solution. Ii desired, buffering compounds can be added to the solution, but they are ordinarily not required and therefore are omitted. The impregnation of the wood is preferably carried to substantial completion, i.-e. the wood is impregnated through and through.-

Suitable woods which can be impregnated and rendered dimensionally stable in accordance with the present invention are the hard and soft woods which can be green or seasoned, exemplary varities being maple, oak, mahogany, hickory, walnut, gum and other hard woods as well as pine, willow,

cypress, spruce, balsam, Douglas fir, and other soft woods.

The impregnation of the wood with the treatment solutions can be carried out by any means which thoroughly saturates the interior of the wood with the solution, such as by long-term soaking in the treatment solution, or the alternate application of vacuum and pressure while the wood is immersed in the treatment solution. For thin items, a simple immersion in the treatment solution for several days, say one to four days, suflices to thoroughly impregnate the wood. Desirably, the wood is presoaked in water for several days in order to thoroughly swell the wood fibers and conserve subsequent treatment solution. The vacuum -pressure method of impregnation, a more rapid method for forcing the treat-,

ment solution throughout the wood, can be carried out by evacuating the wood in a closed vessel to a relatively high vacuum of, for example, 50 to mm. mercury absolute, thereafter admitting treatment solution to the vessel still under vacuum, then releasing the vacuum to atmospheric pressure and if desired superimposing a atmospheres and higher. The evacuation is carried out generally for five to twenty minutes and the atmospheric or higher pressure impregnation is carried out for a similar length of time. After core and the two veneer sheets previously treated as above described were used as the face plies. The press was closed, subjected to a pressure of 150 lbs. per square inch for four minutes while 24 days at C do do 47 days at 0 C 47 days at 0 0.-.. 212 days at 0 C...

. Fresh impregnation by any of the foregoing methods, being heated at 240 F. The press was then the wood is dried to a moisture content of prefopened, the resulting panel and a matched unerably 5 to 20% by weight, either at room temtreated panel were sanded smooth, and both panperature or in a dryer heated to 125 F. to 180 F. els were placed outdoors on a south exposure test or higher. Preferably, the drying is effected while fence in the vertical position for one month. concurrently heating the impregnated wood to a After xp r he treated pl wo remained temperature of 125 to 300 F. or higher, since elelight yellow in color as at the start of the test and vated temperatures hasten the further condensaits surfaces were smooth and free of open checks, tion of methylol ureas in situ in the impregnated while in contrast thereto the untreated plywood wood. panel was reddish brown in color, the surface was Illustrating how the invention may be pracvery rough, and numerous open checks had ticed, the following impregnations of wood were formedcarried out, the results being tabulated in Table I In Table I, runs #1 to #8 show that active sesbelow. Wood veneers, measuring 12" x 12" quimethylol urea is effective at a pH of 5 to 11 in run #1 and measuring 1%" x 1" x 3 in when the solution is freshly prepared, and that the succeeding runs, were presoaked in water for at a p of t 9 superior r sults are secured. two days and then immersed in methylol urea Runs #9 to #15 duplicate r ns #2 to #8 except treatment solutions of the indicated compositions that the treatment solution was aged for 33 days v and concentrations at the indicated pHs and alat room temperatures before being used. Heavy lowed to soak for the indicated length of time. p ipitate was pr se t in ll of t ese latter runs Controls were similarly treated except for the except when the DH was 8.0. Additionally the impregnation. Run Nos. 1 and 16 to 21 were carpercent reduction in dimensional change was not ried out'on Douglas fir veneers, while ru Nos, 2 nearly of the same order as when fresh treatment to 15 were carried out on sap gum veneers. The solution of active sesquimethylol urea was empercentage reduction in dimensional change of p y ns and s w that e q treated wood over untreated wood, measured tanmethylol urea is still active when stored at 0 C. gential to the annual tree growth rings, oven dry for 47 days while the activity is greatly reduced state to water saturated state of samples, is indiwhen stored for as long as 212 days at 0 0. Run cated in the last column of Table I. In the table, #19 shows the inferior results obtained with SMU means -sesquimethylol urea, MMU means monomethylol urea and run #21 shows inferior moncmethylol urea, and DMU means dimethylol results obtained with dimethylol urea. Run #20 urea. is inserted as a comparison with run #21, the

Table I t i in 1'6 116 on st-5! i his??? it Y by titt a Mm rim? treatedwood Fresh 7. i

33 days-..

WWNHODHWWWNNNWWWWWwWWM NIhNOIWOHWWHQQQOOQIQWOIUI ssssssssserrssssssss 1 See note A (exposurejeflt).

Note A.-'The impregnated veneers sheet or run #1 were dried at 110 F. and relative humidity for two days and used to prepare dimensionally stable plywood by the following procedure. An untreated 1%" x 12" x 12" sheet of Douglas fir veneer was used as the core and two veneer sheets treated as in run #1 were used as the face plies to prepare 1%" Douglas flr plywood. A conventional plywood press adapted to be heated was employed, and a commercial urea-formaldehyde hot press adhesive was used at the rate of 20 lbs. per thousand square feet of single glue line. The glue was coated on both sides of the crystalline urea. Thereafter, the solution containing sesquimeth'ylol urea can be evaporated at low temperature to a low moisture content of less than by weight and stored under refrigerated conditions until used, but should be used within about three months. Preferably, sesquirhethylol or other methylol ureas should be fresh- 1y prepared and used immediately.

Various changes may be made in the detailed practice of the invention without departing from the spirit and scope thereof.

What is claimed is:

1. A process for inhibiting dimensional changes in wood induced by moisture and exposure which comprises impregnating such wood with a solution consisting substantially entirely of Water and active methylolureas having a concentration of from 10 to by weight, said methylolureas having from 25 to mole percent of dimethylolurea and '75 to 25 mole percent of monomethylolurea, said solution having a pH of 7 to 9, and thereafter drying the resultant impregnated wood.

2. The process of claim 1 in which the said drying is effected while concurrently heating the impregnated wood to a temperature 01' to 300 F.

3. The process of claim 1 in which the said drying is continued at a temperature of about 125 to 180 F. until the moisture content of the wood reaches about 5% to 20% by weight.

4. The process of claim 1 in which the said methylolureas have 1 /2 methylol groups per urea nucleus.

5. A process for inhibiting dimensional changes in wood induced by moisture and exposure which comprises preparing a solution consisting substantially entirely of water and an equimolar mixture of monomethylolurea and dimethylolurea by dissolving and reacting three moles of dimethylolurea in water with about one mole of urea, said solution having a pH of '7 to 9, and thereafter impregnating wood with the said solution and drying the resultant impregnated wood.

HAMLINE MONROE KVALNES. 

